1. Field of the Invention
The present invention relates to an apparatus and method for recognizing voice. More specifically, the present invention relates to an apparatus and method for recognizing voice without influence of ambient noise.
2. Description of the Prior Art
In a voice recognition apparatus, since voice to be recognized as well as ambient noise are inputted to a microphone, it is important to correctly recognize the voice without influence of the ambient noise.
In U.S. Pat. No 4,239,936 issued on Dec. 16, 1980, for example, a voice recognition system including two microphones is disclosed. The voice to be recognized is inputted to one of the microphones and ambient noise is inputted to the other of the microphones. A voice signal is inputted to a recognition unit to be spectrum-analyzed and an ambient noise signal is inputted to a noise measuring unit such that the strength thereof is measured. When the strength of the ambient noise exceeds a predetermined value, a threshold value is subtracted from a recognition result signal from the recognition unit in a noise rejection unit.
In the above described prior art, it is still impossible to implement noise rejection sufficient for correctly recognizing the voice because it is impossible to reject only the noise signal even if the above described threshold value is used since the two microphones respectively receive the voice to be recognized and the ambient noise. In addition, since the rejection standard is a constant level while the strength of the ambient noise varies, when the strength of the ambient noise is changed, the ambient noise cannot be sufficiently rejected.
Therefore, a principal object of the present invention is to provide a novel apparatus and method for recognizing voice.
Another object of the present invention is to provide an apparatus and method for recognizing voice in which it is possible to further reduce influence of ambient noise.
Another object of the present invention is to provide an apparatus and method for recognizing voice in which it is possible to correctly and surely recognize a voice even if a level of ambient noise varies.
Another object of the present invention is to provide an apparatus and method for recognizing voice in which it is possible to register a reference pattern without influence of ambient noise.
A voice recognizing apparatus in accordance with the present invention has a microphone for inputting voice to a circuit for sampling a voice signal from the microphone exceeding a threshold value. The threshold value is changed in accordance with a level of ambient noise.
A voice recognizing method in accordance with the present invention detects a level of ambient noise; variably sets a threshold level in response to a level of detected ambient noise; and detects a boundary of a voice signal inputted from a microphone in accordance with the threshold value.
In accordance with the present invention, since a threshold value for sampling the voice signal is changed in accordance with a level of the ambient noise, it is possible to correctly recognize the voice inputted from the microphone without influence of the ambient noise even if the level of the ambient noise varies. In addition, if the present invention is utilized for registration of a reference pattern, even if such a reference pattern is registered under a noisy circumstance, it is possible to prevent a reference pattern which is modified by the ambient noise from being registered. Therefore, it is possible to recognize the voice with accuracy.
In one embodiment, after the voice signal from the microphone is sampled in accordance with the threshold value which is determined in accordance with an amplitude of the ambient noise level, a true head and a true tail of the voice to be recognized are detected. Therefore, in accordance with this embodiment, recognition accuracy can be further increased.
In another embodiment, the ambient noise is generated from a loudspeaker by an audio signal from an audio equipment, and therefore, as a signal representative of the ambient noise, the audio signal which is directly inputted from the audio equipment is utilized. In accordance with this embodiment, a further microphone for converting the ambient noise into an electrical signal is not required and also the ambient noise level can be surely detected. However, the ambient noise may be inputted to the further microphone as sound.
In accordance with another embodiment, a feature parameter of the noise is produced and the feature parameter is eliminated from the feature parameter of the voice signal inputted from the microphone, and therefore, a feature parameter pattern for recognition or registration is not affected by the noise.
The objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention when taken in conjunction with accompanying drawings.